package scheduler

import (
	"fmt"
	"log"
	"os"
	"os/signal"
	"sync"
	"syscall"
	"time"

	"git.loafle.net/overflow/probe/service/scheduler/storage"
	"git.loafle.net/overflow/probe/service/scheduler/task"
)

type Scheduler struct {
	taskTargetRegistry *task.TaskTargetRegistry

	tasks   sync.Map
	adapter *storageAdapter

	stopChan chan bool
}

// New will return a new instance of the Scheduler struct.
func New(taskStorage storage.TaskStorage) *Scheduler {
	taskTargetRegistry := &task.TaskTargetRegistry{}

	return &Scheduler{
		taskTargetRegistry: taskTargetRegistry,
		stopChan:           make(chan bool),
		adapter: &storageAdapter{
			taskStorage:        taskStorage,
			taskTargetRegistry: taskTargetRegistry,
		},
	}
}

// RunAt will schedule function to be executed once at the given time.
func (s *Scheduler) RunAt(time time.Time, targetFunc interface{}, params ...interface{}) (string, error) {
	taskTarget, err := s.taskTargetRegistry.Add(targetFunc)
	if err != nil {
		return "", err
	}

	task := task.New(taskTarget, params)
	task.NextRun = time
	s.registerTask(task)

	return task.Hash(), nil
}

// RunAfter executes function once after a specific duration has elapsed.
func (s *Scheduler) RunAfter(duration time.Duration, targetFunc interface{}, params ...interface{}) (string, error) {
	return s.RunAt(time.Now().Add(duration), targetFunc, params...)
}

// RunEvery will schedule function to be executed every time the duration has elapsed.
func (s *Scheduler) RunEvery(duration time.Duration, targetFunc interface{}, params ...interface{}) (string, error) {
	taskTarget, err := s.taskTargetRegistry.Add(targetFunc)
	if err != nil {
		return "", err
	}

	task := task.New(taskTarget, params)
	task.IsRecurring = true
	task.Duration = duration
	task.NextRun = time.Now().Add(duration)
	s.registerTask(task)

	return task.Hash(), nil
}

// Start will run the scheduler's timer and will trigger the execution
// of tasks depending on their schedule.
func (s *Scheduler) Start() error {
	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)

	// Populate tasks from storage
	if err := s.populateTasks(); err != nil {
		return err
	}
	if err := s.persistRegisteredTasks(); err != nil {
		return err
	}
	s.runPending()

	go func() {
		ticker := time.NewTicker(1 * time.Second)
		for {
			select {
			case <-ticker.C:
				s.runPending()
			case <-sigChan:
				s.stopChan <- true
			case <-s.stopChan:
				close(s.stopChan)
			}
		}
	}()

	return nil
}

// Stop will put the scheduler to halt
func (s *Scheduler) Stop() {
	s.stopChan <- true
}

// Wait is a convenience function for blocking until the scheduler is stopped.
func (s *Scheduler) Wait() {
	<-s.stopChan
}

// Cancel is used to cancel the planned execution of a specific task using it's ID.
// The ID is returned when the task was scheduled using RunAt, RunAfter or RunEvery
func (s *Scheduler) Cancel(taskID string) error {
	t, ok := s.tasks.Load(taskID)
	if !ok {
		return fmt.Errorf("Task not found")
	}

	s.adapter.Remove(t.(*task.Task))
	s.tasks.Delete(taskID)
	return nil
}

// Clear will cancel the execution and clear all registered tasks.
func (s *Scheduler) Clear() {
	s.tasks.Range(func(_taskID, _task interface{}) bool {
		s.adapter.Remove(_task.(*task.Task))
		s.tasks.Delete(_taskID.(string))
		return true
	})

	s.taskTargetRegistry = &task.TaskTargetRegistry{}
}

func (s *Scheduler) populateTasks() error {
	tasks, err := s.adapter.Fetch()
	if err != nil {
		return err
	}

	for _, _task := range tasks {
		// If we can't find the function, it's been changed/removed by user
		exists := s.taskTargetRegistry.Exists(_task.TaskTarget.Name)
		if !exists {
			log.Printf("%s was not found, it will be removed\n", _task.TaskTarget.Name)
			_ = s.adapter.Remove(_task)
			continue
		}

		// If the task instance is still registered with the same computed hash then move on.
		// Otherwise, one of the attributes changed and therefore, the task instance should
		// be added to the list of tasks to be executed with the stored params
		_eTask, ok := s.tasks.Load(_task.Hash())
		if !ok {
			log.Printf("Detected a change in attributes of one of the instances of task %s, \n",
				_task.TaskTarget.Name)
			_task.TaskTarget, _ = s.taskTargetRegistry.Get(_task.TaskTarget.Name)
			_eTask = _task
			s.tasks.Store(_task.Hash(), _eTask)
		}
		eTask := _eTask.(*task.Task)

		// Skip task which is not a recurring one and the NextRun has already passed
		if !_task.IsRecurring && _task.NextRun.Before(time.Now()) {
			// We might have a task instance which was executed already.
			// In this case, delete it.
			_ = s.adapter.Remove(_task)
			s.tasks.Delete(_task.Hash())
			continue
		}

		// Duration may have changed for recurring tasks
		if _task.IsRecurring && eTask.Duration != _task.Duration {
			// Reschedule NextRun based on _task.LastRun + registeredTask.Duration
			eTask.NextRun = _task.LastRun.Add(eTask.Duration)
		}
	}
	return nil
}

func (s *Scheduler) persistRegisteredTasks() error {
	var err error
	s.tasks.Range(func(_taskID, _task interface{}) bool {
		err = s.adapter.Add(_task.(*task.Task))
		if nil != err {
			return false
		}
		return true
	})

	return err
}

func (s *Scheduler) runPending() {
	s.tasks.Range(func(_taskID, _task interface{}) bool {
		t := _task.(*task.Task)
		if t.IsDue() {
			go t.Run()
			if !t.IsRecurring {
				s.adapter.Remove(t)
				s.tasks.Delete(t.Hash())
			}
		}
		return true
	})
}

func (s *Scheduler) registerTask(task *task.Task) {
	s.taskTargetRegistry.Add(task.TaskTarget)

	s.tasks.Store(task.Hash(), task)
}